The invention relates to arranging roaming in a telecommunications system comprising a wireless local access network and a public land mobile network (PLMN).
There has been considerable development in recent years in data services provided for mobility-enhancing PLMNs with large coverage areas. The general packet radio service (GPRS) provides GSM networks with efficient data transmission, where radio capacity is only reserved during transfer of packets. A 3G universal mobile telecommunications system (UMTS), standardized by 3GPP (Third Generation Partnership Project), will provide even higher data transmission capacity than GSM/GPRS networks. A radio interface provided by a UMTS terrestrial radio access network (UTRAN) is based on enhanced WCDMA (Wideband Code Division Multiple Access) technology, and a core network is based on the GSM/GPRS core network.
In addition to data services provided by PLMNs, various wireless local area networks have been developed to provide wideband wireless data transmission from a very limited coverage area. An example of such technology is a wireless local area network (WLAN) based on IEEE 802.11. These local networks provide high-speed data transmission and access to the Internet in different hot spots, such as offices or airports. There has also been some convergence of local area networks and PLMNs. For example GSM-based base stations can be used in an office data system to provide a wireless connection to the local area network of the office. On the other hand, WLANs have also been provided with network elements, with which the WLAN can utilize a PLMN. For example WLANs according to the IEEE 802.11 standard, and GSM networks have been provided with network elements for accessing GSM authentication and billing services via a WLAN.
Roaming can also be arranged in a WLAN, i.e. a user can be authenticated in the local network where he is roaming (and with which he typically has no service contract made in advance) by means of the PLMN, a subscriber identification module (in the GSM a subscriber identity module SIM) provided by the home PLMN (HPLMN), and subscriber data located in the subscriber's home network. However, a mobile station can also be located for example abroad in the area of a local network with no direct connection to the subscriber's HPLMN but only to one or more networks of other PLMN operators. In order to provide successful roaming in such a situation, PLMN operators must have mutual roaming agreements determining how a roaming subscriber is to be charged. When a roaming mobile station contacts a local network, it is not necessarily aware of the PLMNs that are available via the local network in question. In such a case, the mobile station must provide the local network with the network identifier (PLMN ID) of its HPLMN operator. Based thereon, the local network should select the PLMN that the roaming user should use. For this purpose, the local network should store data about the PLMNs where the user can roam, and preferably also data on the preferred PLMNs. This would require additional functionality and increase the need for memory capacity in the local network, and it might also cause conflicts of interest between the PLMN operators and the operators of local area networks.